Number of ports: this has to be considered especially if you will need to charge more that one device at a time. When it has a bigger battery, then you will discover that it may have more parts to make it possible to charge more than one phone or multiple gadgets at a time.
Cable: Each device has to come with a cable to facilitate charging. This can be a USB standard cable or the micro USB cable. It is important to know that it has to be charged beforehand. Some come with extra cables. This can be an important addition as it can help if you need to charge multiple devices at the same time.